MLA

Agnes Ledgerwood Hately Wilson, Vernon, Indiana, Letter to James Kinnier Wilson, Bridgeton?, New Jersey. 1878. https://collections.library.yale.edu/catalog/16719927.

APA, 6th edition

Agnes Ledgerwood Hately Wilson, Vernon, Indiana, letter to James Kinnier Wilson, Bridgeton?, New Jersey. (1878). [Correspondence, Manuscripts]. https://collections.library.yale.edu/catalog/16719927.